chapter 38: angiosperm reproduction. chapter 38 assignment
TRANSCRIPT
CHAPTER 38: ANGIOSPERM
REPRODUCTION
CHAPTER 38 ASSIGNMENT
• Angiosperm flowers can attract pollinators using visual cues and volatile chemicals
• Many angiosperms reproduce sexually and asexually
• Symbiotic relationships are common between plants and other species
OVERVIEW: FLOWERS OF DECEIT
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38.1 FLOWERS, DOUBLE FERTILIZATION, AND FRUITS
ARE UNIQUE FEATURES OF THE ANGIOSPERM LIFE CYCLE
Sporophyte – plant that produces haploid spores through MEIOSIS
Gametophyte – haploid spores divide through MITOSIS to produce a plant that produces gametes
REPRODUCTIVE TERMINOLOGY
• Diploid (2n) sporophytes produce spores (n) by meiosis
• These grow into haploid (n) gametophytes
• Gametophytes produce haploid (n) gametes by mitosis
• Fertilization of gametes produces a sporophyte (diploid)
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• In angiosperms, the sporophyte is the dominant generation, the large plant that we see
• The gametophytes are reduced in size and depend on the sporophyte for nutrients
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Fig. 38-2b
Anther
Pollen tube
Germinated pollen grain (n)(male gametophyte)
Ovary
Ovule
Embryo sac (n)(female gametophyte)
Egg (n)
Sperm (n)
Zygote(2n)
Seed
SeedEmbryo (2n)(sporophyte)
Simple fruit
Germinatingseed
Mature sporophyteplant (2n)
(b) Simplified angiosperm life cycle
Key
Haploid (n)
Diploid (2n)
FERTILIZATION
• Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle
• Flowers consist of four floral organs: sepals, petals, stamens, and carpels
FLOWER STRUCTURE AND FUNCTION
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• A stamen consists of a filament topped by an anther with pollen sacs that produce pollen
• A carpel has a long style with a stigma on which pollen may land
• At the base of the style is an ovary containing one or more ovules
• A single carpel or group of fused carpels is called a pistil
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Fig. 38-2a
Stamen Anther
Filament
Stigma CarpelStyle
Ovary
Receptacle
SepalPetal
(a) Structure of an idealized flower
• Complete flowers contain all four floral organs
• Incomplete flowers lack one or more floral organs (stamens or carpels)
• Clusters of flowers are called inflorescences
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Fig. 38-3(a)
Development of a malegametophyte (in pollen grain)
Microsporangium(pollen sac)
Microsporocyte (2n)
4 microspores (n)
Each of 4microspores (n)
Malegametophyte
Generative cell (n)
Ovule
(b) Development of a femalegametophyte (embryo sac)
Megasporangium (2n)
Megasporocyte (2n)
Integuments (2n)
Micropyle
MEIOSIS
Survivingmegaspore (n)
3 antipodal cells (n)
2 polar nuclei (n)
1 egg (n)
2 synergids (n)
Fem
ale gam
etop
hyte
(emb
ryo sa
c)
Ovule
Embryosac
Integuments (2n)
Ragweedpollengrain
Nucleus oftube cell (n)
MITOSIS
100
µm
20 µm
75 µm
• Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers
• If pollination succeeds, a pollen grain produces a pollen tube that grows down into the ovary and discharges sperm near the embryo sac
• The pollen grain consists of the two-celled male gametophyte and the spore wall
DEVELOPMENT OF MALE GAMETOPHYTES IN POLLEN GRAINS
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Fig. 38-3a(a) Development of a male
gametophyte (in pollen grain)
Microsporangium(pollen sac)
Microsporocyte (2n)
4 microspores (n)
Each of 4microspores (n)
Malegametophyte
Generative cell (n)
MEIOSIS
Ragweedpollengrain
Nucleus oftube cell (n)
MITOSIS
20 µm
75 µm
• Within an ovule, megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes
DEVELOPMENT OF FEMALE GAMETOPHYTES (EMBRYO SACS)
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Fig. 38-3b
Ovule
(b) Development of a femalegametophyte (embryo sac)
Megasporangium (2n)
Megasporocyte (2n)
Integuments (2n)
Micropyle
MEIOSIS
Survivingmegaspore (n)
3 antipodal cells (n)
2 polar nuclei (n)
1 egg (n)
2 synergids (n)
Fem
ale gam
etop
hyte
(emb
ryo sa
c)
Ovule
Embryosac
Integuments (2n)
MITOSIS
100
µm
• In angiosperms, pollination is the transfer of pollen from an anther to a stigma
• Modes of pollination:• Wind• Water• Insects: bee, moth and butterfly, fly• Bird• Bat
POLLINATION
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Fig. 38-4a
Abiotic Pollination by Wind
Hazel staminate flowers(stamens only)
Hazel carpellate flower(carpels only)
Fig. 38-4b
Pollination by Bees
Common dandelion undernormal light
Common dandelion underultraviolet light
Fig. 38-4c
Pollination by Moths and Butterflies
Moth on yucca flower
Anther
Stigma
Fig. 38-4d
Pollination by Flies
Blowfly on carrion flower
Fly egg
Fig. 38-4e
Hummingbird drinking nectar of poro flower
Pollination by Birds
Fig. 38-4f
Long-nosed bat feeding on cactus flower at night
Pollination by Bats
• After landing on a receptive stigma, a pollen grain produces a pollen tube that extends between the cells of the style toward the ovary
• Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac
• One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm
DOUBLE FERTILIZATION
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Fig. 38-5a
Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule
Micropyle Egg
Pollen grain
Polar nuclei
Fig. 38-5b
Ovule
Polar nuclei
Egg
Synergid
2 sperm
Fig. 38-5c
Endospermnucleus (3n)(2 polar nucleiplus sperm)
Zygote (2n)(egg plus sperm)
Fig. 38-6
Wild-type Arabidopsis
Micropyle Ovule
Pollen tubegrowing towardmicropyle
Seed stalkMany pollentubes outsideseed stalk
Seed stalk
20 µ
m
Ovule
pop2 mutant Arabidopsis
EXPERIMENT
• After double fertilization, each ovule develops into a seed
• The ovary develops into a fruit enclosing the seed(s)
SEED DEVELOPMENT, FORM, AND FUNCTION
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• Endosperm development usually precedes embryo development
• In most monocots and some eudicots, endosperm stores nutrients that can be used by the seedling
• In other eudicots, the food reserves of the endosperm are exported to the cotyledons
ENDOSPERM DEVELOPMENT
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• The first mitotic division of the zygote is transverse, splitting the fertilized egg into a basal cell and a terminal cell
EMBRYO DEVELOPMENT
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Fig. 38-7
Ovule
Endospermnucleus
Integuments
Zygote
Zygote
Terminal cellBasal cell
Basal cell
ProembryoSuspensor
Cotyledons
Shootapex
Rootapex Seed coat
EndospermSuspensor
• The embryo and its food supply are enclosed by a hard, protective seed coat
• The seed enters a state of dormancy
STRUCTURE OF THE MATURE SEED
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• In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two thick cotyledons (seed leaves)
• Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl
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Fig. 38-8a
Epicotyl
Hypocotyl
Cotyledons
Radicle
Seed coat
(a) Common garden bean, a eudicot with thick cotyledons
• The seeds of some eudicots, such as castor beans, have thin cotyledons
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Fig. 38-8b
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
• A monocot embryo has one cotyledon• Grasses, such as maize and wheat, have a special cotyledon called a scutellum
• Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root
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Fig. 38-8c
(c) Maize, a monocot
Scutellum(cotyledon)
Pericarp fusedwith seed coat
Endosperm
Epicotyl
Hypocotyl
Coleoptile
RadicleColeorhiza
• Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling
• The breaking of seed dormancy often requires environmental cues, such as temperature or lighting changes
SEED DORMANCY: AN ADAPTATION FOR TOUGH TIMES
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• Germination depends on imbibition, the uptake of water due to low water potential of the dry seed
• The radicle (embryonic root) emerges first
• Next, the shoot tip breaks through the soil surface
SEED GERMINATION AND SEEDLING DEVELOPMENT
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• In many eudicots, a hook forms in the hypocotyl, and growth pushes the hook above ground
• The hook straightens and pulls the cotyledons and shoot tip up
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Fig. 38-9a
(a) Common garden bean
Seed coat
Radicle
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Epicotyl
Foliage leaves
Cotyledon
Hypocotyl
• In maize and other grasses, which are monocots, the coleoptile pushes up through the soil
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Fig. 38-9b
(b) Maize
Radicle
Foliage leaves
ColeoptileColeoptile
• A fruit develops from the ovary• It protects the enclosed seeds and aids in seed dispersal by wind or animals
• A fruit may be classified as dry, if the ovary dries out at maturity, or fleshy, if the ovary becomes thick, soft, and sweet at maturity
FRUIT FORM AND FUNCTION
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• Fruits are also classified by their development: Simple, a single or several fused carpels Aggregate, a single flower with multiple separate carpels Multiple, a group of flowers called an inflorescence
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Fig. 38-10
FlowerStamenCarpels
Ovary
Stigma
Pea flowerOvule
Seed
Carpel(fruitlet)
Raspberry flower
Stigma
Ovary
Stamen
Stamen
Pineapple inflorescence Apple flower
Stigma
Stamen
Ovule
Each segmentdevelopsfrom thecarpelof oneflower
Pea fruit Raspberry fruit Pineapple fruit Apple fruit
(a) Simple fruit (b) Aggregate fruit (c) Multiple fruit (d) Accessory fruit
Sepal
Petal Style
Ovary(in receptacle)
Sepals
Seed
Receptacle
Remains ofstamens and styles
Fig. 38-10a
Ovary
Stigma
Pea flowerOvule
Seed
Stamen
Pea fruit
(a) Simple fruit
Fig. 38-10b
StamenCarpels
Carpel(fruitlet)
Raspberry flower
Stigma
Ovary
Stamen
Raspberry fruit
(b) Aggregate fruit
Fig. 38-10c
Flower
Pineapple inflorescence
Each segmentdevelopsfrom thecarpelof oneflower
Pineapple fruit
(c) Multiple fruit
• An accessory fruit contains other floral parts in addition to ovaries
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Fig. 38-10d
Apple flower
Stigma
Stamen
Ovule
Apple fruit
(d) Accessory fruit
Sepal
Petal Style
Ovary(in receptacle)
Sepals
Seed
Receptacle
Remains ofstamens and styles
• Fruit dispersal mechanisms include:WaterWindAnimals
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Fig. 38-11a
Coconut
Dispersal by Water
Fig. 38-11b
Tumbleweed
Dispersal by Wind
Winged fruit of maple
Dandelion “parachute”Winged seedof Asianclimbing gourd
Fig. 38-11c
Dispersal by Animals
Seeds carried toant nest
Seeds buried in caches
Seeds in fecesBarbed fruit